Single thickness blade with leading edge serrations on an axial fan

ABSTRACT

A fan with a hub, one or more single thickness fan blades coupled to the hub, each single thickness fan blade having a length L 1  and a width W, a single relative thickness, a plurality of serrations over a length L 2  of a leading edge.

RELATED APPLICATIONS

This application claims benefit of and priority to U.S. Provisional Patent Application No. 62/213,576, filed on Sep. 2, 2015, which is hereby incorporated by reference for all purposes as if set forth herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to fans, and more specifically to a single thickness blade on an axial fan with leading edge serrations that generate lower levels of sound.

BACKGROUND OF THE INVENTION

Propellers generate sound waves as they rotate. These sound waves are both a source of energy loss as well as detrimental to the user experience. However, earlier attempts to reduce such sound waves have met with limited success. In addition, propellers are more rigid than other structures, and do not have similar design constraints.

SUMMARY OF THE INVENTION

An axial fan is disclosed that has a hub and one or more fan blades coupled to the hub. Each fan blade has a length L₁ and a width W, a single relative thickness, and a plurality of serrations over a length L₂ of a leading edge. By using the disclosed ratios of length to width, serration configuration and other disclosed features, the amount of noise generated can be reduced.

Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings might be to scale, but emphasis is instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views, and in which:

FIG. 1 is a graph showing a sound power profile for an axial fan with single thickness blades with leading edge serrations, as compared with an axial fan with single thickness blades without leading edge serrations;

FIG. 2 is a graph showing a sound power profile for an axial fan with single thickness blades with leading edge serrations, as compared with an axial fan with single thickness blades without leading edge serrations;

FIG. 3 is a diagram of a single thickness fan blade with leading edge serrations, in accordance with an exemplary embodiment of the present disclosure;

FIG. 4 is a diagram of a three blade fan with single-thickness fan blades having leading edge serrations, in accordance with an exemplary embodiment of the present disclosure;

FIG. 5 is a diagram of a four blade fan with single-thickness fan blades having leading edge serrations, in accordance with an exemplary embodiment of the present disclosure; and

FIG. 6 is a diagram of a five blade fan with single-thickness fan blades having leading edge serrations, in accordance with an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals. The drawing figures might be to scale and certain components can be shown in generalized or schematic form and identified by commercial designations in the interest of clarity and conciseness.

As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, phrases such as “between X and Y” and “between about X and Y” should be interpreted to include X and Y. As used herein, phrases such as “between about X and Y” mean “between about X and about Y.” As used herein, phrases such as “from about X to Y” mean “from about X to about Y.” The term “approximately” means that the range of values associated with the cited value may vary as a function of explicit or implicit tolerances of measurements, and where no specific limitation is provided, that the range of values may extend to encompass any range of values that is not disclosed in the prior art.

FIG. 1 is a graph 100 showing a sound power profile for an axial fan with single thickness blades with leading edge serrations, as compared with an axial fan with single thickness blades without leading edge serrations. As used herein, “single thickness” means that the thickness of the fan blade is approximately uniform, subject to normal manufacturing variations in thickness, or other minor variations that may from time to time be introduced by design or manufacture. The data for graph 100 was generated using a five blade fan rotating in air at a speed of approximately 1180 RPM, where each of the five fan blades were serrated in the manner shown in FIG. 3.

As can be seen in graph, the use of serrations results in a substantial sound power reduction for a frequency band that is most associated with the range of human hearing, namely approximately 250 to 5,000 Hz, relative to a fan with five blades that are not serrated. Furthermore, the absolute reduction of sound power L_(W) in dB is essentially the same for the frequency range from approximately 500 Hz to 2,500 Hz. As such, it can be seen that the leading edge serrations of the fan blade reduce sound generation that can be a nuisance or hazard to the user, reduce vibrations associated with sound generation that can cause mechanical wear and high-cycle fatigue, and provide other benefits that are readily apparent to one of skill in the art.

FIG. 2 is a graph 200 showing a sound power profile for an axial fan with single thickness blades with leading edge serrations, as compared with an axial fan with single thickness blades without leading edge serrations.

The data for graph 200 was generated using a three blade fan rotating in air at a speed of approximately 850 RPM, where each of the three fan blades were serrated in the manner shown in FIG. 3.

As can be seen in graph, the use of serrations results in a substantial sound power reduction for a smaller frequency band that is most associated with the range of human hearing, namely approximately 1,000 to 2,500 Hz, relative to a fan with three blades that are not serrated. Furthermore, the absolute reduction of sound power L_(W) in dB is essentially the same over that frequency range. Graph 200 demonstrates that the reduction in sound power loss is greater at higher speeds and for larger numbers of fan blades.

FIG. 3 is a diagram of a single thickness fan blade 300 with leading edge serrations 302, in accordance with an exemplary embodiment of the present disclosure. The shape of fan blade 300 is exemplary, and variations in the number and size of the single thickness fan blades, the shape and size of the serrations and other design features are contemplated as falling within the scope of the present disclosure. Fan blade 300 was used to generate the data shown in FIGS. 1 and 2.

Leading edge serrations 302 have a saw-tooth pattern with no spacing between each individual serration, which is approximately triangular in shape. While a straight edge section can be provided between each triangular serration, the disclosed configuration results in the best observed reduction in sound power loss for a single thickness fan blade having the relative dimensions shown.

Fan blade 300 has a relative overall length L₁, and a relative width W that is approximately uniform along the length L₁. The approximate ratio of the length L₁ to the width W is 2:1, but other suitable ratios can also or alternatively be used without departing from the teachings of the present disclosure. Likewise, the width can vary as a function of the length, the blade can have a varying length, or other suitable configurations can also or alternatively be used. Edge serrations 302 are disposed on a leading edge of fan blade 300, such that they impact the air as fan blade 300 spins and cause formation of stream-wise vortices, which reduce tonal noise and randomize wake vortex shedding. The randomized wake vortex shedding also results in decreased sound power generation in trailing fan blades, as demonstrated by the greater reduction in sound power loss as a function of number of blades and rotation speed as shown in graphs 100 and 200.

Edge serrations 302 have an even spacing S and a saw-tooth form, and extend for a length L₂ that is approximately equal to width W. The approximate ratio of the length L₂ to the width W is 1:1, but other suitable ratios can also or alternatively be used without departing from the teachings of the present disclosure. Edge serrations 302 extend along the straight portion of the leading of blade 300, and the width of blade 300 gradually reduces by approximately 40% as blade 300 extends towards the end that is coupled to a hub (not explicitly shown). Alternatively, the serrations can vary along the length of the edge, can be uniformly spaced, can be spaced by varying amounts, can be of uniform or non-uniform size or spacing, the leading edge of the blade can have an arc or spline, or the blade can have other suitable configurations, although the advantages disclosed herein are known to be present for a blade having the disclosed dimensions and parameters. Bolt holes 304 are used to secure fan blade 300 to a hub assembly. Fan blades of equivalent shape and size but lacking serrations 302 were also used to generate the data in graphs 100 and 200 for the fans without serrations. The relative dimensions and ratios of fan blade 300 are thus operative in obtaining the noise reductions shown in graphs 100 and 200.

FIG. 4 is a diagram of a three blade fan 400 with single thickness fan blades having leading edge serrations, in accordance with an exemplary embodiment of the present disclosure. Three blade fan 400 includes fan blades 402, 404 and 406, and hub assembly 408, which has spokes 410, 412 and 414 that are coupled to fan blades 402, 404 and 406 using bolts, rivets, spot welds or in other suitable manners. The shape of the fan blades is exemplary, and variations in the number and size of the single thickness fan blades, the shape and size of the serrations and other design features are contemplated as falling within the scope of the present disclosure. While such variations are contemplated, it has also been shown in graphs 100 and 200 that the design for fan blade 300 with the specific serration configuration and relative length and width dimensions shown results in a decrease in sound power loss and sound generation, which decrease is more significant as the speed of rotation and number of blades increases. The shape of the fan blades is exemplary, and variations in the shape and size of the serrations and other design features are contemplated as falling within the scope of the present disclosure. For example, two or one of the blades can have serrations and the rest can be smooth, where suitable, the type and spacing of serrations can vary from blade to blade, or other suitable configurations can also or alternatively be used.

In particular, three blade fan 400 was used to generate the data shown in graph 200, and has a fan blade design that is identical to that used to generate the data shown in graph 100, except that a five blade fan was used to generate the data for graph 100. Because the fan blade designs were not varied, it has been established that increasing the number of fan blades and the rotation speed results in a greater reduction in the sound power reduction for single thickness fans made using fan blade 300.

FIG. 5 is a diagram of a four blade fan 500 with single thickness fan blades having leading edge serrations, in accordance with an exemplary embodiment of the present disclosure. Four blade fan 500 includes fan blades 502, 504, 506 and 508, and hub assembly 510, which has spokes 512, 514, 516 and 518 that are coupled to fan blades 502, 504, 506 and 508 using bolts, rivets, spot welds or in other suitable manners. The shape of the fan blades is exemplary, and variations in the shape and size of the serrations and other design features are contemplated as falling within the scope of the present disclosure. For example, three, two or only one of the blades can have serrations and the rest can be smooth, where suitable, the type and spacing of serrations can vary from blade to blade, or other suitable configurations can also or alternatively be used.

FIG. 6 is a diagram of a five blade fan 600 with single thickness fan blades having leading edge serrations, in accordance with an exemplary embodiment of the present disclosure. Five blade fan 600 includes fan blades 602, 604, 606, 608 and 610, and hub assembly 612, which has spokes 614, 616, 618, 620 and 622 that are coupled to fan blades 602, 604, 606, 608 and 610 using bolts, rivets, spot welds or in other suitable manners. The shape of the fan blades is exemplary, and variations in the number and size of the fan blades, the shape and size of the serrations and other design features are contemplated as falling within the scope of the present disclosure. For example, four, three, two or one of the blades can have serrations and the rest can be smooth, where suitable, the type and spacing of serrations can vary from blade to blade, or other suitable configurations can also or alternatively be used.

It should be emphasized that the above-described embodiments are merely examples of possible implementations. Many variations and modifications may be made to the above-described embodiments without departing from the principles of the present disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. 

What is claimed is:
 1. A fan, comprising: a hub; one or more single thickness fan blades coupled to the hub, each single thickness fan blade having a length L₁ and a width W, and further comprising: a single relative thickness; and a plurality of serrations over a length L₂ of a leading edge.
 2. The fan of claim 1 wherein the ratio of the width W to length L₂ is approximately unity.
 3. The fan of claim 1 wherein the width W is approximately uniform along the length L₁ of each of the single thickness fan blades.
 4. The fan of claim 1 wherein the plurality of serrations for each of the single thickness fan blades have a spacing S.
 5. The fan of claim 1 wherein the plurality of serrations for each of the single thickness fan blades are formed by a saw-tooth pattern with no spacing between each individual serration.
 6. The fan of claim 1 wherein the plurality of serrations for each of the single thickness fan blades are formed along a straight section of the leading edge.
 7. The fan of claim 1 where the plurality of serrations for each of the single thickness fan blades are formed along a section of each of the fan blades that has the width W.
 8. The fan of claim 1 wherein each of the single thickness fan blades further comprises a plurality of holes for securing the blade to the hub.
 9. The fan of claim 1 wherein each of the single thickness fan blades is secured to the hub by one of bolts, rivets or spot welds.
 10. The fan of claim 1 wherein the plurality of serrations reduce a sound power for sound frequencies between 125 Hz and 5000 Hz relative to a fan with fan blades having no serrations.
 11. A fan, comprising: a hub having two or more spokes; two or more fan blades, each coupled to one of the spokes of the hub, each fan blade having a length L₁ and a width W, and further comprising: a single relative thickness; and a plurality of serrations over a length L₂ of a leading edge.
 12. The fan of claim 11 wherein the ratio of the width W to length L₂ is approximately unity.
 13. The fan of claim 11 wherein the width W is approximately uniform along the length L₁ of each of the fan blades.
 14. The fan of claim 11 wherein the plurality of serrations for each of the fan blades have a spacing S.
 15. The fan of claim 11 wherein the plurality of serrations for each of the fan blades are formed by a saw-tooth pattern with no spacing between each individual serration.
 16. The fan of claim 11 wherein the plurality of serrations for each of the fan blades are formed along a straight section of the leading edge.
 17. The fan of claim 11 wherein the plurality of serrations for each of the fan blades are formed along a section of each of the fan blades that has the width W.
 18. The fan of claim 11 wherein each of the fan blades further comprises a plurality of holes for securing the blade to the hub.
 19. The fan of claim 11 wherein each of the fan blades is secured to the hub by one of bolts, rivets or spot welds.
 20. A fan, comprising: a hub having a plurality of spokes; one or more single thickness fan blades, each coupled to one of the spokes of the hub, each single thickness fan blade having a length L₁ and a width W, and further comprising: a single relative thickness; and a plurality of serrations over a length L₂ of a leading edge; wherein the ratio of the width W to length L₂ is approximately unity, the width W is approximately uniform along the length L₁ of each of the single thickness fan blades, the plurality of serrations for each of the single thickness fan blades have a spacing S, the plurality of serrations for each of the single thickness fan blades are formed by a saw-tooth pattern with no spacing between each individual serration, the plurality of serrations for each of the single thickness fan blades are formed along a straight section of the leading edge, the plurality of serrations for each of the single thickness fan blades are formed along a section of each of the single thickness fan blades that has the width W, each of the blades further comprises a plurality of holes for securing the single thickness fan blade to the hub, and each of the single thickness fan blades is secured to the hub by one of bolts, rivets or spot welds. 